Field of the Invention
This invention relates to a terminal device, a mail transmission system, and a transmission method, and particularly to a terminal device, a mail transmission system, and a transmission method for mail transmission of a file with a digital signature.
Description of the Related Art
A technique for mail transmission of a file with a digital signature is available. Recently, a scanner, a printer, or an MFP (Multi-Functional Peripheral) which is combination of the former has a communication function, so that a file with a digital signature can be transmitted via mail from an image forming apparatus.
In mail transmission of a file with a digital signature in an office or the like, approval by another user as an authorizer such as a supervisor may be required. Namely, a user who transmits a file may be different from an authorizer.
In such a case, as one method, such a method that a user asks an authorizer to attach a digital signature to a file of interest in a personal computer or the like and then to perform an operation for mail transmission is exemplified. Alternatively, such a method that, in the case of using an image forming apparatus, an authorizer who has been asked uses his/her own log-in information to log in an image forming apparatus, to attach a digital signature, and then to perform an operation for mail transmission is also exemplified.
As a method for approval of an authorization key, for example, Japanese Laid-Open Patent Publication No. 2010-278482 discloses such a technique that, even when an encryption key used for a digital signature is revealed, by generating a substitute verification key by using an interaction algorithm, another verification key valid for that digital signature is generated so as not to invalidate the digital signature.
As set forth above, when a user who transmits a file with a digital signature is different from an authorizer, the authorizer has had to perform an operation for approval or an operation for mail transmission, which has been bothersome.